1. Field of the Invention
The current invention relates to a packaging unit for a glass wound on a winding shaft, and also to the use of said packaging unit.
2. Description of the Related Art
Thin glass is increasingly being used for diverse applications, for example in the field of consumer electronics. As cover glasses for semiconductors, organic LED-light sources, thin indicator devices or in the field or regenerative energies or energy technology such as solar cells. Examples for this are touch panels, capacitors, thin film batteries, flexible printed circuit boards, flexible OLED's, flexible photovoltaic modules or e-papers. Thin glass is coming increasingly into focus for many applications, due to its outstanding characteristics, such as resistance to chemicals, temperature changes and heat, gas tightness, high electric insulation properties, customized coefficient of expansion, pliability, high optical quality and light transparency or also high surface quality with very little roughness due to a fire polished surface. Thin glass is understood to be a glass panel, glass web or a glass film or glass substrate with thicknesses of less than approximately 1.2 mm to thicknesses of approximately 1 to 15 μm, such as 5 to 15 μm. Due to its pliability, thin glass is increasingly wound after its fabrication and stored in the form of a glass roll, or transported in roll form for packaging or further processing. Compared to storing and transporting flat material, wound glass offers the advantage of cheaper, more compact storage, transport and handing in further processing.
In order to further reduce transportation and storage costs it is advantageous to wind radii that are as tight as possible, which increases tensile stresses in the glass ribbon and thereby the risk of breakage.
With all of the outstanding characteristics, glass as a brittle material has a rather low breaking resistance since it is less resistant to tensile stresses. For breakage-free storage and for breakage-free transportation of such a glass roll, the quality and integrity of the edges are firstly of importance in order to avoid origination of a crack or breakage in the wound glass ribbon. Even damage such as tiny fissures or microscopic cracks or chipping at the edge can become the cause for large cracks or breakage in the glass ribbon. In a wound up state, the top side of the glass ribbon is subject to tensile stress, which is why integrity and freedom of the surface of the glass ribbon from scratches, grooves or other surface defects is important in order to avoid the development of a crack or break in the wound thin glass. Thirdly, manufacture related interior stresses in the glass should be minimized, or nonexistent, in order to avoid development of a crack or break in the wound glass ribbon. Since in commercial manufacturing all three factors can only be optimized to a limited extent, the vulnerability of breaks occurring in such a wound glass is further increased relative to the already existing limits of its material properties. Special precautions and conditions are therefore important for storage and transportation of such a glass roll in order to avoid damage to the glass. A glass roll of this type must be protected in particular from jolts and vibration-related stresses. Such mechanical stresses acting from the outside could lead to exceeding the breaking limit of the glass and could therefore result in the formation of cracks in the glass. If, for example, a glass roll is placed directly onto a storage surface, such as a pallet, in a position where the axis progresses approximately horizontally, then the problem exists that a stress concentration occurs in the contact region, thus easily causing fractures in the glass.
Highly sensitive goods such as thin glass on a roll are very vulnerable during transport, the primary influences being maximum acceleration peaks as well as vibrations. In transport packaging solutions where the transported good is vibration-decoupled from the packaging, resonances occur which increase the acting acceleration many times over.
For transport logistic reasons, the packaging of a glass roll should be able to be handled as simply as possible; should be able to be easily loaded and unloaded with the glass roll that is to be protected; its volume and weight to be as low as possible; and be inexpensive and be recyclable or disposable in an environmentally friendly manner.
Storage, transport and handling of sheet glass materials is crucial with thicker glasses which are not pliable enough to be wound, such as flat glasses and known glasses for flat screens. Packaging for such sheet glass materials is described, for example, in US 2007/0131574 or JP 048577/1990. Such packaging, however is not compact and is totally unsuitable for packaging of a glass roll.
Packaging of a wound material on a roll is described in WO 2008/123124. Here, a plate-shaped flange component having an attached tubular part which engages into the hollow space of a winding core is described for protection against jolts for both sides of the roll. The two parts should always be integral, formed from polyolefin-bead foam which is intended to absorb the impact energy. Furthermore, a space is provided for the protection of the edges between the upper edge of the wound material and each flange. This type of packaging is however unsuitable for a glass roll since on the one hand, the glass roll would be entirely unprotected in its surface expansion between the flanges, and on the other hand vibrational energy and impact energy would be introduced into the glass in an unacceptable manner, in spite of the provided space and the material selected for the roll support. Moreover, no secure option for storage and transportation of a multitude of glass rolls is provided.
In a further development, JP 2009-173307 describes a form of packaging for storage and transportation of a sensitive pressure measuring sheet wound on a winding core, wherein a flange which is larger in size than an outside diameter of the wound pressure measuring sheet is provided at each end of the roll core around which the measuring sheet is wound. The pressure measuring sheet is hereby arranged at a distance from the placement surface. A glass film, in contrast to a pressure measuring sheet, is a material which breaks easily. This means, that in the case of a pressure measuring sheet, it is sufficient to ensure that the microcapsules formed on the surface for pressure measurements do not burst, however in the case of wound glass it is necessary to ensure that no breaks occur on the surface of the roll or at the edges of the glass ribbon which form the lateral regions of the roll or, respectively, the thin glass. Since, in particular, it may be the case that the two lateral regions of the roll are exposed outwardly with the edges of the glass ribbon, they may easily become a starting point for breaks at the edges.
WO 2010/38760 describes a further development for a glass roll. For a glass roll wound on a winding core having lateral flanges, various arrangements for buffering with buffering material which is being introduced between the lateral regions of the glass roll and the flanges are described. It is hereby intended that contact between the edges of the glass ribbon and the flanges, which could lead to breaks, is thus avoided.
For this purpose, laterally protruding intermediate layers wound in between the glass ribbon layers are proposed which fill only part of the space and which are not in contact with the flanges or which—in another proposed embodiment—are in contact with the flanges. However, cracks or breaks may form in the glass ribbon or at the edges during winding or unwinding of the glass roll if the protruding regions of the intermediate layer interlock or catch on each other. Jolts or oscillations during transport may also lead to lateral movement of the glass ribbon layers, which likewise leads to breaks of the glass ribbon, or to edge damage. A lateral movement of the glass ribbon may occur hereby in its entirety along the axial direction of the winding core or in that the outer layers of the glass ribbon move laterally on the roll relative to the inner layers of the glass ribbon, causing the edge of the glass ribbon to then be arranged above one another in a step-like manner, in the sense of “telescoping”.
In another arrangement a separate buffer material is arranged between the glass roll and flange. Lateral movement of the glass ribbon layers on the roll caused by jolts or vibrations during transport could hereby be reduced. However, in particular in the case of transport-related vibrations, a relative movement between glass ribbon edges and such buffer material will result. Even very small relative movements or stresses caused thereby at the edges of the glass ribbon can result in damage to said edges or can introduce cracks into the glass ribbon.
In order to avoid this it is proposed in another embodiment to arrange the buffer material to make contact only with the flange, but to have no contact with the lateral regions of the glass roll. However, here again, a lateral movement of the glass ribbon layers on the roll as a whole or a lateral telescoping may occur due to jolts or vibrations during transport, again causing breaks in the glass ribbon or edge damage.
WO 2010/038760 moreover describes the design of an axis, extended on both sides and protruding beyond the flanges which are supported on mounts in the form of pedestals. This is intended to prevent rotation of the glass roll independently of the flanges. Such a structure or a plurality of such structures may also be covered by a packaging crate. A disadvantage of this solution is, however, that jolts and vibration-related stresses are transferred onto or into the glass roll in an undamped state which represents a high risk for breaks or cracks in the glass. The glass roll is also not protected against vibrations, jolts and relative movement in horizontal or vertical direction, or against rotation. This type of packaging can moreover only be loaded and unloaded from two sides, which represents a significant restriction in regard to handling and logistics.
Alternatively to this packaging wherein the glass roll is oriented transversely, a packaging is described wherein the glass roll is oriented vertically. Here, a plurality of glass rolls is placed with their winding cores on vertically positioned column-type elements which are fixed to the floor of a crate body. However, wobbling of the glass rolls during transport presents a disadvantage. Even though—in order to prevent breakages of the glass ribbon thus caused—sufficient spacing between the glass rolls or the provision of a buffer material between the glass rolls is suggested, the edges on the supporting face of the glass roll are being stressed in an improper manner, not only due to the inherent pressure of the glass roll, but in particular also due to wobbling of the roll, which leads to cracks and breaks in the glass ribbon and to damaged edges. Moreover, jolts and vibration related stresses are also transferred in this case undamped to the glass roll, representing a high risk for breakages or cracks for the glass.
It is therefore the objective of the current invention to avoid the previously described disadvantages and to provide a packaging unit to accommodate glass wound on a winding core at a reasonable cost and which is easy to handle and wherein the risk of breakage or crack formation in the glass during storage or transport is reduced. The packaging unit can also permit loading and unloading from four sides.